Date: Wed, 26 Mar 2008 22:12:00 +0000 (UTC) From: Poul-Henning Kamp <phk@FreeBSD.org> To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org Subject: cvs commit: src/sys/amd64/conf NOTES src/sys/amd64/isa clock.c src/sys/conf options.amd64 options.i386 options.pc98 src/sys/i386/conf NOTES src/sys/i386/isa clock.c src/sys/pc98/cbus clock.c src/sys/pc98/conf NOTES Message-ID: <200803262212.m2QMC0Yj000551@repoman.freebsd.org>
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phk 2008-03-26 22:12:00 UTC
FreeBSD src repository
Modified files:
sys/amd64/conf NOTES
sys/amd64/isa clock.c
sys/conf options.amd64 options.i386 options.pc98
sys/i386/conf NOTES
sys/i386/isa clock.c
sys/pc98/cbus clock.c
sys/pc98/conf NOTES
Log:
Back in the good old days, PC's had random pieces of rock for
frequency generation and what frequency the generated was anyones
guess.
In general the 32.768kHz RTC clock x-tal was the best, because that
was a regular wrist-watch Xtal, whereas the X-tal generating the
ISA bus frequency was much lower quality, often costing as much as
several cents a piece, so it made good sense to check the ISA bus
frequency against the RTC clock.
The other relevant property of those machines, is that they
typically had no more than 16MB RAM.
These days, CPU chips croak if their clocks are not tightly within
specs and all necessary frequencies are derived from the master
crystal by means if PLL's.
Considering that it takes on average 1.5 second to calibrate the
frequency of the i8254 counter, that more likely than not, we will
not actually use the result of the calibration, and as the final
clincher, we seldom use the i8254 for anything besides BEL in
syscons anyway, it has become time to drop the calibration code.
If you need to tell the system what frequency your i8254 runs,
you can do so from the loader using hw.i8254.freq or using the
sysctl kern.timecounter.tc.i8254.frequency.
Revision Changes Path
1.77 +0 -13 src/sys/amd64/conf/NOTES
1.241 +0 -112 src/sys/amd64/isa/clock.c
1.31 +0 -2 src/sys/conf/options.amd64
1.240 +0 -2 src/sys/conf/options.i386
1.202 +0 -2 src/sys/conf/options.pc98
1.1252 +0 -13 src/sys/i386/conf/NOTES
1.245 +0 -122 src/sys/i386/isa/clock.c
1.166 +0 -98 src/sys/pc98/cbus/clock.c
1.87 +0 -17 src/sys/pc98/conf/NOTES
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